In copending application Ser. No. 168,877 filed July 14, 1980, entitled PHOTOCHEMICAL REACTION CAVITY by the same inventor as the present application and assigned to the same assignee, there is described an optical cavity for use in a process for enriching uranium by increasing the percentage of U.sub.235. Laser beams of two different frequencies are used to produce a photochemical reaction in which an atom of fluorine is stripped from a molecule of UF.sub.6, a gas, to precipitate out UF.sub.5 which is a solid. The UF.sub.5 powder, which has a higher concentration of U.sub.235 isotopes, must then be refluorinated to produce UF.sub.6 gas also having a higher concentration of U.sub.235 isotopes. This basic enrichment process has been described in the literature. See, for example, the brochure, "Introduction to Laser Isotope Separation" published by the Los Alamos Scientific Laboratory, publication LASL-78-13 of the Applied Photochemistry Division.